1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive comprising a voice coil motor having a yoke with a multiple-bend magnetic flux conductor.
2. Description of the Prior Art
Computer systems typically comprise a disk drive comprising one or more disks rotated about a center axis by a spindle motor, and a head coupled to the distal end of an actuator arm which is actuated radially over the surface of the disk by a voice coil motor. The surface of the disk is coated with a magnetic material which is magnetized by the head in order to record digital data on the disk. The digital data modulates a current in a write coil of the head in order to write magnetic transitions representing the recorded data in concentric, radially spaced tracks. During read back, the head senses the magnetic transitions to generate an analog read signal comprising pulses representing the recorded digital data, wherein the pulses are demodulated into digital data transmitted to the host computer system.
Prior art voice coil motors typically employ a yoke comprised of a top and bottom trapezoidal plates for housing top and bottom trapezoidal magnets for generating a first magnetic flux guided through the plates and through an air gap between the magnets. A trapezoidal voice coil is inserted into the air gap and a current applied to the voice coil generates a second magnetic flux interacting orthogonally with the first magnetic flux. The orthogonal interaction of the magnetic fluxes creates a torque which rotates the actuator arm about a pivot so as to position the head radially over the disk.
The two plate, two magnetic prior art voice coil motors are expensive to manufacture and install into the disk drive. The top and bottom magnets are typically manufactured with a center polarity boundary to generate the first magnetic flux bi-directionally (up and down), wherein the xe2x80x9cupxe2x80x9d magnetic flux interacts with a first side of the trapezoidal voice coil, and the xe2x80x9cdownxe2x80x9d magnetic flux interacts with a second side of the trapezoidal voice coil. Magnetizing the magnets with the appropriate polarity boundary increases the expense of the magnets. In addition, generating the bi-directional flux requires a magnet of sufficient size, which further increases the manufacturing cost of the voice coil motor. Still further, installing the trapezoidal plates requires a three step process: connecting the bottom plate to the base of the disk drive, installing the voice coil and actuator arm onto a pivot, and connecting the top plate to the bottom plate forming the air gap between the magnets. This three step process increases the manufacturing time and expense of the disk drive.
The above-referenced patent application entitled xe2x80x9cDISK DRIVE EMPLOYING A VOICE COIL MOTOR COMPRISING A YOKE FOR GENERATING A UNIDIRECTIONAL MAGNETIC FLUX AND A VOICE COIL PARTIALLY INTERACTING WITH THE UNIDIRECTIONAL MAGNETIC FLUXxe2x80x9d discloses a voice coil motor employing a yoke comprising a unitary U-shaped magnetic flux conductor comprising top and bottom magnets for generating a unidirectional magnetic flux. The unidirectional magnetic flux interacts with only one side of a trapezoidal voice coil wherein the second side of the voice coil acts only as a return path for the current. This reduces the manufacturing expense of the voice coil motor since it obviates the need to magnetize the magnets with a center polarity boundary. Further, the amount of magnetic material is reduced to essentially half that of the conventional trapezoidal two plate design described above. Still further, installing the voice coil motor involves a less expensive and less time consuming two step process: connecting the U-shaped magnetic flux conductor to the base of the disk drive, and installing the voice coil and actuator arm onto a pivot and rotating the trapezoidal voice coil into the air gap between the magnets.
FIG. 1A shows a top, perspective view of a U-shaped magnetic flux conductor 2 employed in the above-referenced patent application. As shown in the side view of FIG. 1B, the U-shaped magnetic flux conductor 2 comprises a body having a top protruding plate portion 4A and a bottom protruding plate portion 4B. A magnet 6 is attached to an interior surface of the top plate portion 4A for generating the unidirectional magnetic flux 8 conducted through the U-shaped magnetic flux conductor 2 and through an air gap 10 formed between the magnet 6 and the second protruding plate portion 4B. A first side of a trapezoidal voice coil interacts with the unidirectional magnetic flux 8 to generate the torque for rotating the actuator arm about the pivot, and a second side of the trapezoidal coil acts as a return path for the current.
Since air has a high reluctance, it is desirable to bend the U-shaped magnetic flux conductor 2 into a small radius so as to minimize the width of the air gap 10, thereby enhancing performance of the voice coil motor. In addition, it is desirable to manufacture the U-shaped magnetic flux conductor 2 with sufficient thickness so as to prevent the magnetic flux 8 from saturating the magnetic flux conductor 2. However, the thickness of the magnetic flux conductor 2 limits the bend radius before cracks 12 will manifest about the bend as illustrated as dashed lines in FIG. 1B. Thus, the thickness of the magnetic flux conductor 2 and relative strength of the magnet 6 limits the minimum width of the air gap 10.
There is, therefore, a need to reduce the air gap in a voice coil motor employing a yoke manufactured by bending a magnetic flux conductor to form an air gap without cracking the magnetic flux conductor about the bend.
The present invention may be regarded as a disk drive comprising an actuator arm, a head coupled to the actuator arm, and a voice coil motor for actuating the actuator arm to move the head. The voice coil motor comprises a first magnet for generating a first magnetic flux, and a yoke comprising a magnetic flux conductor for guiding the first magnetic flux. The magnetic flux conductor comprising a body and a top and bottom protruding plate portions, wherein the body and the plate portions are integrally formed. Each plate portion extends away from the body, and the top plate portion is vertically spaced-apart from the bottom plate portion. The body defines, in vertical cross section, a primary bend having a primary bend radius and at least one secondary bend having a secondary bend radius, wherein the secondary bend radius is non-concentric with the primary bend radius. The voice coil motor further comprises a voice coil for conducting a current to generate a second magnetic flux for interacting at least partially with the first magnetic flux.
In one embodiment, the magnetic flux conductor comprises a substantially U-shape. In another embodiment, the secondary bend comprises a plurality of contiguous secondary bends, and in another embodiment the secondary bend comprises a plurality of non-contiguous secondary bends. In yet another embodiment, the voice coil motor further comprises a second magnet attached to the top plate portion of the magnetic flux conductor, and the first magnet is attached to the bottom plate portion of the magnetic flux conductor. In one embodiment, the voice coil comprises a trapezoidal shape comprising a first side and a second side, the first side for conducting the current to generate at least part of the second magnetic flux for interacting with the first magnetic flux, and the second side for returning the current to the first side and for generating at least part of the second magnetic flux not substantially interacting with any magnetic flux. In an alternative embodiment, the voice coil is wrapped around the top plate portion of the magnetic flux conductor.
The present invention may also be regarded as a yoke for use in a voice coil motor of a disk drive, the disk drive comprising an actuator arm and a head coupled to the actuator arm. The voice coil motor comprises a first magnet for generating a first magnetic flux, and the yoke comprises a magnetic flux conductor for guiding the first magnetic flux. The magnetic flux conductor comprising a body and a top and bottom protruding plate portions, wherein the body and the plate portions are integrally formed. Each plate portion extends away from the body, and the top plate portion is vertically spaced-apart from the bottom plate portion. The body defines, in vertical cross section, a primary bend having a primary bend radius and at least one secondary bend having a secondary bend radius, wherein the secondary bend radius is non-concentric with the primary bend radius.